Water vapor distributions measured with the Michelson Interferometer for Passive Atmospheric Sounding on board Envisat (MIPAS/Envisat)



[1] We present water vapor profiles obtained from infrared limb emission measurements recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European Environmental Satellite (Envisat). These retrievals are based on constrained nonlinear least squares fitting. The retrievals are very sensitive to the radiative signals of thin transparent clouds and measurements showing any signature of cloud contamination have been rigorously excluded. The vertical resolution of the retrieved water vapor profiles is 4.5 to 6.5 km up to an altitude of approximately 42 km. The resulting total error of the retrieved water vapor profiles, including measurement noise, systematic and random parameter uncertainties like interfering species or preretrieved temperature or spectroscopic data, is in the range of 6 to 9% in the stratosphere. Towards the tropopause, the error increases up to 30% due to the exponential gradient of the tropospheric water vapor profile, where small line of sight uncertainties lead to strong absolute variations in the water vapor profile below the hygropause. Averaged water vapor distributions obtained from measurements taken during 11 days in June, July, and August 2003 show the expected distributions with low water vapor volume mixing ratios (VMRs) above the tropopause, comparatively dry air inside the tropical stratospheric updraft region and indications for strong dehydration above the Antarctic continent inside the polar vortex. Additionally, in the transition from tropics to subtropics, a latitude band was observed where, in higher altitudes, large water vapor VMRs were measured compared to adjacent tropical and midlatitudinal regions. Especially over the Arabic peninsula, a moist region at 18 km altitude was observed, which was probably related to the South Asian monsoon circulation.